1. Field of the Invention
The invention relates to an apparatus for preparing chemicals, and in particular to a method and apparatus for preparing hydroxymethylfurfural (HMF).
2. Description of the Related Art
Oil reserves in the world are gradually being depleted. Meanwhile, the greenhouse effect is continuously growing. Europe, America and Japan have developed a policy, wherein before the year 2020, some materials utilized in plastic consumer products must be derived from renewable resources. Thus, research into using biomass raw materials to refine chemical raw materials has become popular. For the BREW and BIOMASS biomass energy development plan, Europe and the United States designated hydroxymethylfurfural (HMF) and its derivatives, 2,5-Furandicarboxylic acid (FDCA), as an important cyclic building block applied on furanic polyester and furanic polyamide biomass plastic products. The intermediate products of hydroxymethylfurfural (HMF) downstream derivatives comprise chemical intermediate products of tetrahydrofuran, synthetic solvents of enamel or resin solvents and raw materials of organic synthesis, in particular, raw materials of pyrrole and thiophene syntheses. In the future, the raw materials for preparing hydroxymethylfurfural (HMF) will be derived from sugar produced by cellulose bio-hydrolysis business technology, which is expected in 2015.
Hydroxymethylfurfural (HMF) is a kind of furfural compound. Hydroxymethylfurfural (HMF) is prepared merely by chemical methods utilizing hexose conversion but not by bio-fermentation methods due to inhibition on microorganism growth in solutions. However, in such chemical methods, it is difficult to control side reactions and separate hydroxymethylfurfural (HMF), resulting in low reaction efficiency and high costs. Thus, related downstream applications of HMF have yet to be successfully commercialized. The reasons causing low hydroxymethylfurfural (HMF) production efficiency comprise the polymerization of hydroxymethylfurfural (HMF) to form humins under a high temperature and in an acidic condition, hydrolysis of hydroxymethylfurfural (HMF) to form levulinic acid under a high temperature and in acidic aqueous solution, and occurrence of a crossed aldol reaction between hydroxymethylfurfural (HMF) and sugar to form humins under a high temperature.
Lewkowski (ARKIVOC 2001) summarizes four hydroxymethylfurfural (HMF) preparation methods comprising a homogeneous aqueous solution reaction process with a temperature of less than 200° C., a homogeneous aqueous solution reaction process with a temperature exceeding 200° C., an organic solution reaction process, and a two-phase reaction process. In the homogeneous aqueous solution reaction process (less than 200° C.), the yield of hydroxymethylfurfural (HMF) is merely 30%. Also, in another homogeneous aqueous solution reaction process (exceeding 200° C.), the yield of hydroxymethylfurfural (HMF) is merely 58%. The organic solution reaction process prevents hydroxymethylfurfural (HMF) from hydrolyzing to form levulinic acid. Szmant published the method comprising utilizing boron trifluoride ether complexes (BF3.Et2O) as a catalyst, sugar and dimethyl sulfoxide (DMSO) to prepare hydroxymethylfurfural (HMF) in 1981 (J. Chem. Tech. Biotechnol.). For the method taught by Szmant, that was capable of achieving a yield exceeding 90%, was merely fructose. Further, boron trifluoride ether complexes (BF3.Et2O) are corrosive, expensive and unable to be reused, such that wastewater may be produced, and it is difficult to separate hydroxymethylfurfural (HMF) from dimethyl sulfoxide (DMSO). Thus, the method cannot be commercialized. Archer-Daniels-Midland Co. (U.S. Pat. No. 7,317,116 B2, 2008) discloses the method comprising utilizing high fructose syrup, N-Methyl-2-Pyrrolidone (NMP) or dimethylacetamide (DMAc) and a solid-state catalyst to prepare hydroxymethylfurfural (HMF). However, it is also difficult to separate hydroxymethylfurfural (HMF) from N-Methyl-2-Pyrrolidone (NMP). In the two-phase reaction process, hydroxymethylfurfural (HMF) is continuously extracted from a water phase containing mineral acids at 177° C. through an organic solvent undissolved with water to improve main product yields. However, provision of large amounts of organic solvents and considerable energy to separate hydroxymethylfurfural (HMF) from a mixing solution containing dilute hydroxymethylfurfural (HMF) is required. Also, corrosiveness exists for the method.
In order to reduce side reactions and further commercialized technology, some well-known chemical companies such as Dupont, Merk & Co, Canon KK, FURCHIM and Roquette, and research institutions such as Battelle and the University of Wisconsin are trying to overcome the technical barrier of a low hydroxymethylfurfural (HMF) yield. For instance, Roquette (U.S. Pat. No. 4,590,283, 1986) discloses the method comprising utilizing 20% fructose, dimethyl sulfoxide (DMSO) and AMBERLIT C200 cation resin as a catalyst for reaction at 80° C. and simultaneously utilizing methyl isobutyl ketone (MIBK) to extract hydroxymethylfurfural (HMF) to prepare hydroxymethylfurfural (HMF). Although its yield achieves 97%, 8 hrs of reaction time is consumed. In particular, methyl isobutyl ketone (MIBK) contains merely 2% of dilute hydroxymethylfurfural (HMF). Thus, recovering large amounts of solvents is required, increasing costs. Additionally, the University of Wisconsin discloses the method comprising adding an organic solvent dissolved with hydroxymethylfurfural (HMF) and undissolved with water to an aqueous phase to form a two-phase reaction to reduce hydroxymethylfurfural (HMF) to contact with water to hydrolyze to form levulinic acid. Although the reaction time thereof is only 3 min, its hydroxymethylfurfural (HMF) yield is merely 75%.